Published on Web 08/04/2007
Mechanism of Nitrite Formation by Nitrate Photolysis in Aqueous Solutions: The Role of Peroxynitrite, Nitrogen Dioxide, and Hydroxyl Radical Sara Goldstein* and Joseph Rabani Contribution from the Department of Physical Chemistry, The Hebrew UniVersity of Jerusalem, Jerusalem 91904, Israel Received May 20, 2007; E-mail:
[email protected] Abstract: Photolysis of aqueous NO3- with λ g 195 nm is known to induce the formation of NO2- and O2 as the only stable products. The mechanism of NO3- photolysis, however, is complex, and there is still uncertainty about the primary photoprocesses and subsequent reactions. This is, in part, due to photoisomerization of NO3- to ONOO- at λ < 280 nm, followed by the formation of •OH and •NO2 through the decomposition of ONOOH (pKa ) 6.5-6.8). Because of incomplete information concerning the mechanism of peroxynitrite (ONOOH/ONOO-) decomposition, previous studies were unable to account for all observations. In the present study aqueous nitrate solutions were photolyzed by monochromatic light in the range of 205-300 nm. It is shown that the main primary processes at this wavelength range hν
hν
are NO3- 98 •NO2 + O•- (reaction 1) and NO3- 98 ONOO- (reaction 2). Based on recent knowledge on the mechanisms of peroxynitrite decomposition and its reactions with reactive nitrogen and oxygen species, we determined Φ(1) and Φ(2) using different experimental approaches. Both quantum yields increase with decreasing the excitation wavelength, approaching Φ(1) ) 0.13 and Φ(2) ) 0.28 at 205 nm. It is also shown that the yield of nitrite increases with decreasing the excitation wavelength. The implications of these results on UV disinfection of drinking water are discussed.
Introduction
It is well-known that the overall stable products resulting from the photolysis of aqueous NO3- at λ g 195 nm are NO2- and O2.1-3 The mechanism of NO3- photolysis is complex, and there is still uncertainty about the primary photoprocesses and subsequent reactions.3-6 This is in part due to the photoisomerization of NO3- to ONOO- and the formation of •OH and •NO through the decomposition of ONOOH (pK ) 6.5-6.8).7 2 a Because of incomplete information concerning the mechanism of peroxynitrite (ONOOH/ONOO-) decomposition, previous studies were unable to account for all observations. Only recently, with renewed interest in peroxynitrite promoted by its important role in biological systems,8,9 has the detailed reaction mechanism been elucidated,7 motivating us to revisit this system. (1) Shuali, H.; Ottolenghi, M.; Rabani, J.; Yelin, Z. J. Phys. Chem. 1969, 73, 3445-3451. (2) Barat, F.; Gilles, L.; Hickel, B.; Sutton, J. J. Chem. Soc. A 1970, 19821986. (3) Mack, J.; Bolton, J. R. J. Photochem. Photobiol., A 1999, 128, 1-13. (4) Mark, G.; Korth, H.-G.; Schuchmann, H.-P.; von Sonntag, C. J. Photochem. Photobiol., A 1996, 101, 89-103. (5) Sharpless, C. M.; Linden, K. G. EnViron. Sci. Technol. 2001, 35, 29492955. (6) Madsen, D.; Larsen, J.; Jensen, S. K.; Keiding, S. R.; Thogersen, J. J. Am. Chem. Soc. 2003, 125, 15571-15576. (7) Goldstein, S.; Lind, J.; Merenyi, G. Chem. ReV. 2005, 105, 2457-2470. (8) Beckman, J. S.; Beckman, T. W.; Chen, J.; Marshall, P. A.; Freeman, B. A. Proc. Natl. Acad. Sci. U.S.A. 1990, 87, 1620-1624. (9) Radi, R.; Peluffo, G.; Alvarez, M. N.; Naviliat, M.; Cayota, A. Free Radical Biol. Med. 2001, 30, 463-488. 10.1021/ja073609+ CCC: $37.00 © 2007 American Chemical Society
The absorption spectrum of NO3- is dominant by a weak n f π* band around 302 nm ( ) 7.2 M-1 cm-1) and a much stronger π f π* band at 200 nm ( ) 9900 M-1 cm-1). It has been suggested that excitation in the π f π* band (λ < 280 nm) proceeds via the two primary photoprocesses 1 and 2, whereas excitation in the n f π* band (λ > 280 nm) proceeds through 1 and 3.3 hν
NO3- 98 •NO2 + O•-
(O•- + H2O h •OH + OH-) (1) hν
NO3- 98 ONOO-
(2)
hν
NO3- 98 NO2- + O•
(3)
Flash-photolysis studies at the 200 nm band provide evidence for the formation of ONOO-, •NO2, and •OH.1,2 However, a recent femtosecond transient absorption spectroscopy shows the formation of ONOO- with Φ ) 0.48 and [NO + O2]- with Φ ) 0.08 within 2 ps.6 This suggests that •NO2, observed in the flash photolysis, is produced by subsequent reactions. In any case, the main contribution to nitrite formation at λ < 280 nm is through the decomposition of peroxynitrite. ONOOH decays almost entirely into nitrate with kd ) 1.25 ( 0.05 s-1 at 25 °C,10,11 whereas ONOO- is relatively stable. Upon increasing the pH, nitrite and O2 at a ratio 2:1 are formed at the expense of nitrate. At pH 9-10 the yield of nitrite amounts to about 80% of the initial peroxynitrite.12-14 These results can be J. AM. CHEM. SOC. 2007, 129, 10597-10601
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a
All rate constants are taken from ref 7 except k5 (ref 16).
rationalized by assuming the homolysis of ONOOH and homolytic equilibrium of ONOO- (Scheme 1) followed by subsequent radical reactions (not shown in Scheme 1), e.g., the reaction of •OH with ONOO- and NO2-, the reaction of •NO2 with O2•- and •NO, hydrolysis of •NO2. Evidently, the overall rates of the different reaction paths strongly depend on the experimental conditions.7 The homolytic equilibrium between ONOO- and •NO + O2•has not yet been considered as an important reaction pathway during the photolysis of NO3-. This homolytic equilibrium contributes to the yield of nitrite since the reaction of •NO2 with •NO forms N O , which hydrolyzes to NO -, and that with O •2 3 2 2 produces O2NOO-, which decomposes into NO2- and O2.15 The formation of •OH radicals both by the photolysis of NO3- and decomposition of ONOOH makes the system sensitive to the presence of organic impurities, as most organic materials react efficiently with •OH. Further complication results when the solutions are contaminated with CO2, which lowers the nitrite yield by catalyzing the decomposition of ONOO- into NO3(Scheme 1, reaction 5).16,17 In the present study we determined Φ(1) and Φ(2) in nitrate solutions excited by monochromatic light in the range of 205300 nm using different experimental approaches, which take into consideration the complexity of the system as described above and in more detail in a recent review.7 The implications of the present results on UV disinfection of drinking water are also discussed. Experimental Section Materials. All chemicals were of the highest available purity. Solutions were prepared with deionized water, which was treated using a Milli-Q water purification system. Nitrate solutions were prepared by dissolving the appropriate amount of NaNO3 (Merck 99.5%) and NaH2PO4 (Mallinckrodt 99.9%), and the pH was adjusted with solutions of HClO4 (J. T. Baker 69-72%) or NaOH (1 M, J. T. Baker). The Griess reagent (modified) was purchased from Sigma. Analysis. The concentration of peroxynitrite was determined from its absorption using 302 ) 1670 M-1 cm-1.18 The concentration of nitrite was determined by mixing equal volumes of the sample and the Griess reagent. The absorption at 540 nm was read after 15 min against nonirradiated sample. Calibration was carried out using aqueous (10) Kissner, R.; Nauser, T.; Bugnon, P.; Lye, P. G.; Koppenol, W. H. Chem. Res. Toxicol. 1997, 10, 1285-1292. (11) Merenyi, G.; Lind, J.; Goldstein, S.; Czapski, G. J. Phys. Chem. A 1999, 103, 5685-5691. (12) Pfeiffer, S.; Gorren, A. C. F.; Schmidt, K.; Werner, E. R.; Hansert, B.; Bohle, D. S.; Mayer, B. J. Biol. Chem. 1997, 272, 3465-3470. (13) Kirsch, M.; Korth, H.-G.; Wensing, A.; Sustmann, R.; de Groot, H. Arch. Biochem. Biophys. 2003, 418, 133-150. (14) Lymar, S. V.; Khairutdinov, R. F.; Hurst, J. K. Inorg. Chem. 2003, 42, 5259-5266. (15) Logager, T.; Sehested, K. J. Phys. Chem. 1993, 97, 10047-10052. (16) Lymar, S. V.; Hurst, J. K. J. Am. Chem. Soc. 1995, 117, 8867-8868. (17) Uppu, R. M.; Squadrito, G. L.; Pryor, W. A. Arch. Biochem. Biophys. 1996, 327, 335-343. (18) Hughes, M. N.; Nicklin, H. G. J. Chem. Soc. A 1968, 450-452. 10598 J. AM. CHEM. SOC.
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solutions containing known concentrations of nitrite. Formaldehyde was determined using the Nash reagent (2 M ammonium acetate, 0.05 M acetic acid, 0.02 M acetylacetone).19 The reagent was mixed with an equal volume of the tested solution, and after incubation for about 15 min at 50 °C, the concentration of formaldehyde was determined from its absorption using 412 ) 8000 M-1 cm-1.19 Photolysis. Irradiations were carried out in cylindrical cells (2 cm i.d., 1 or 2 cm length) made from Suprasil quartz under magnetic stirring at room temperature (24 ( 1 °C). The light entered through a flat optical window. The 1 cm long cell was used with the xenon light source, and the 2 cm long cell was used with the mercury lamp. The cells had short side arms with glass taper joints, through which the solutions were introduced. A small stirrer was placed in the solutions outside the light path. The volumes of the illuminated solutions (including a small amount in the side arms, corrected for the stirrer) were measured as 3.07 and 6.67 mL, respectively. This was calculated from the difference in the weight of the cell, stirrer, and stopper with and without water. Two light sources were used: (i) A monochromatic low-pressure mercury lamp (Heraeus NNI 120/44U, with the 185 nm line filtered out). The monochromatic light passed through a 10 cm long tube located between the lamp and the sample. The incident light intensity was controlled by changing the distance between the lamp and the sample. (ii) A xenon lamp (Osram 150 W ozone-free) coupled with a monochromator (SX-17MV setup from Applied Photophysics). The incident light density was measured with a calibrated Si photosensor (Hamamatsu S2281) coupled with a Keithley 617 programmable electrometer and by the iodide-iodate actinometer.20 An iodideiodate actinometer was daily prepared. It contained 0.6 M potassium iodide and 0.1 M potassium iodate in 0.01 M Na2B4O7‚12 H2O, at pH 9.25 (all three products of Sigma-Aldrich, reagent grade). We have recently redetermined the quantum yields of I3-, and the values used in the present study are 0.92 at 205-240 nm, 0.72 at 253.7 nm, 0.53 at 260 nm, 0.42 at 270 nm, and 0.28 at 300 nm.21 Direct measurements of scattered light was done by comparing between the light signal at a given wavelength to that observed when the monochromator is set to 170 nm (where the light intensity is practically zero). This showed only 0.6% scattered light at 300 nm increasing to about 13% at 205 nm. Using the photosensor, the absorbed light was corrected for the scattered light and also by 4%, which accounts for the reflection of the incident light from the surface of the quartz cell. No corrections were done using the iodide-iodate actinometer as it is assumed that scattered light is from long wavelengths where both aqueous nitrate and iodide-iodate actinometer solutions are optically transparent. This assumption was verified using narrow band interference filters (1012 nm) at 205 and 214 nm with 14% and 22% peak transmittance, respectively. The light absorbed by nitrate solutions was calculated using Beer’s law. Modeling of the experimental results was carried out using INTKIN, a noncommercial program developed at Brookhaven National Laboratories by Dr. H. A. Schwarz.
Results and Discussion
The apparent rate constants of the decay of ONOO- are 3.2 × 10-5 and 1.3 × 10-5 s-1 at pH 12 and 13, respectively, at 25 °C, independent of peroxynitrite concentration.11 Hence, the half-life of ONOO- at pH g 12 is longer than 6 h enabling its accurate detection within less than 10 min of radiation. 2-Propanol (20 mM) was added to the alkaline nitrate to protect ONOO- from its reaction with •OH. 2-Propanol was chosen as an •OH scavenger because in aerated solutions the products of this reaction are acetone and O2•-. Acetone reacts slowly with ONOO-, i.e., k ) 0.066 and 0.02 s-1 at pH 12 and 13, (19) Nash, T. Biochem. J. 1953, 55, 416-421. (20) Rahn, R. O.; Stefan, M. I.; Bolton, J. R.; Goren, E.; Shaw, P. S.; Lykke, K. R. Photochem. Photobiol. 2003, 78, 146-152. (21) Goldstein, S.; Rabani, J. J. Photochem. Photobiol., in press, 2007.
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Scheme 2. Reaction Mechanism for the Production of NO2- in Acidic Solutions Containing HCO2- or CH3OH
Scheme 3. Mechanism of Peroxynitrite Decomposition in the Absence of 2-Propanol
Figure 1. Formation of nitrite upon photolysis of aerated solutions containing (b) 0.1 M NO3-, 0.02 M CH3OH, 0.01 M PB, pH 6.1; (O) 0.02 M NO3-, 0.02 M CH3OH, 0.01 M PB, pH 6.0; (2) 0.1 M NO3-, 0.01 M HCO2-, pH 4.7. The absorbed dose rate varied between 1.72 × 10-8 and 1.08 × 10-6 einstein L-1 s-1.
respectively,22 while no measurable reaction of O2•- with ONOO- has been reported. Although carbonate is usually present as a contaminant in alkaline solutions, it has no effect on the decomposition of peroxynitrite because the concentration of the active form CO2 at pH g 12 is negligible. Hence, under these conditions Φ(ONOO-)2-propanol ) Φ(2). The total quantum yield of the •OH radical, produced both by the decomposition of peroxynitrite and as a possible primary product, was determined by measuring the formation yield of NO2- in the presence of HCO2Na or CH3OH in acidic solutions. Under such conditions, the reactions of HCO2- with peroxynitrite is relatively slow23 and does not compete with the selfdecomposition of peroxynitrite. Although the reaction of •OH with HCO2- in aerated solutions forms O2•- and CO2, the latter reacts fast only with ONOO-,16 and therefore it does not affect the yield of NO2-. The reaction of •OH with CH3OH in aerated solutions forms O2•- and H2CdO. As will be shown below, the reaction of H2CdO with ONOO- does not compete with the faster self-decomposition of peroxynitrite at this pH range. The reaction mechanism for the production of NO2- in acidic solutions containing HCO2- or CH3OH is described in Scheme 2. Scheme 2 shows that the yield of NO2- equals the total yield of •OH. The homolysis of ONOOH produces about 28% •OH and •NO2,14,24 and therefore, Φ(NO2-) ) Φ(1) + 0.28Φ(2). Thus, knowing the values of Φ(2) ) Φ(ONOO-)2-propanol and Φ(NO2-) allows the calculation of Φ(1). A different experimental approach to determine Φ(1) is based on measurements of peroxynitrite yield at pH 13 in the presence and absence of 2-propanol.4 This approach has the advantage that all the relevant data is at the same pH, whereas in the first approach Φ(2) measured in alkaline solution is coupled with nitrite measured in acidic solution for the derivation of Φ(1). The mechanism of peroxynitrite decomposition in the absence of 2-propanol is described in Scheme 3. Each pair of •OH and •NO produced by reaction 1 destroys one ONOO- ion 2 irrespective on the distribution of •OH between reactions 8 and (22) Merenyi, G.; Lind, J.; Goldstein, S. J. Am. Chem. Soc. 2002, 124, 40-48. (23) Goldstein, S.; Czapski, G. J. Am. Chem. Soc. 1998, 120, 3458-3463. (24) Hodges, G. R.; Ingold, K. U. J. Am. Chem. Soc. 1999, 121, 10695-10701.
9: If •OH is converted to •NO2 by reaction with NO2-, the resulting •NO2 pair destroys one ONOO- ion through the removal of •NO and O2•- (eq 6). The same result is obtained upon reaction of •OH with ONOO- according to eq 8 because the produced •NO reacts with •NO2 so that the net effect is the removal of one ONOO- ion by the •OH radical. Hence, Φ(1) ) Φ(ONOO-)2-propanol - Φ(ONOO-)no propanol. Note that if reaction 1 does not take place, as suggested by Madsen et al.,6 the yield of peroxynitrite at pH 13 should not be affected by the presence of 2-propanol. Photolysis at 253.7 nm Using the Low-Pressure Mercury Lamp. The yield of nitrite was determined upon photolysis of aerated aqueous solutions containing 0.02 or 0.1 M NaNO3 and 0.01 M PB (phosphate buffer). Some of the experiments were carried out in the presence of 0.02 M CH3OH at pH 5.9-6.2, whereas others were carried out in the presence of 0.01 M HCO2Na at pH 4.7 yielding similar results (see below). The yield of nitrite was below the detection limit when a cutoff filter, which eliminates the light below 270 nm, was used indicating that the contribution of light from higher wavelengths is negligible. The yield of nitrite was independent of the incident light intensity and NO3- concentration. It increased linearly with the absorbed dose yielding the same quantum yield in the presence of HCO2- or CH3OH (Figure 1). From the slope of the line in Figure 1 Φ(NO2-) ) 0.065 ( 0.002 was derived. In the presence of CH3OH, Φ(NO2-) ≈ Φ(H2CdO) implying that under our experimental conditions H2CdO does not react with peroxynitrite. The concentration of ONOO- was measured immediately after photolysis of aerated solutions containing 0.05 or 0.1 M NaNO3, 0.02 M 2-propanol, and 0.01 or 0.1 M NaOH. The experiments in the absence of 2-propanol were carried out in the presence of 0.1 M NaNO3 and 0.1 M NaOH. The concentration of ONOO- increased linearly with the absorbed dose as demonstrated in Figure 2. The quantum yields of peroxynitrite were determined from the slopes of the lines in Figure 2 as Φ(ONOO-)2-propanol ) Φ(2) ) 0.102 ( 0.002 and Φ(ONOO-)no propanol ) 0.065 ( 0.002. Hence, the first approach, where Φ(NO2-) ) Φ(1) + 0.28Φ(2) yields Φ(1) ) 0.036 ( 0.004. The second approach, where Φ(1) ) Φ(ONOO-)2-propanol - Φ(ONOO-)no propanol, yields almost the same Φ(1) ) 0.037 ( 0.004. Since the first approach is based on measurements of J. AM. CHEM. SOC.
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light by the accumulated ONOO- (255(ONOO-) ∼ 500 M-1 cm-1).25 The photolysis of ONOO- results in the formation of •NO and O2•- (reaction 11),10 which recombine fast back to ONOO(eq 6), so that the net role of ONOO- is an inner filter effect. hν
ONOO- 98 •NO + O2•-
Figure 2. Formation of peroxynitrite formed upon photolysis of aerated solutions containing (b) 0.05 or 0.1 M NO3-, 0.02 M 2-propanol, 0.1 M NaOH; (O) 0.05 or 0.1 M NO3-, 0.02 M 2-propanol, 0.01 M NaOH; (2) 0.1 M NO3-, 0.1 M NaOH. The absorbed dose rate varied between 8.06 × 10-7 and 1.34 × 10-6 einstein L-1 s-1.
Figure 3. Formation of peroxynitrite upon photolysis of aerated solutions containing 0.1 M NO3-, 0.02 M 2-propanol, and 0.1 M NaOH. The incident light intensity varied between 9.3 × 10-7 and 1.16 × 10-6 einstein L-1 s-1. The solid line is the simulated yield of ONOO- using Φ(2) ) 0.102, 253.7(ONOO-) ) 550 M-1 cm-1, 253.7(NO3-) ) 4.25 M-1 cm-1, and kd ) 1.3 × 10-5 s-1 for the spontaneous decomposition of peroxynitrite.
nitrite and peroxynitrite at pH 4.7-6.2 and 13, respectively, whereas the other approach uses data at pH 13, the similar Φ(1) values indicate that the quantum yields are pH-independent. The similar Φ(1) also support once again that ONOOH undergoes homolysis forming about 28% •OH and •NO2 radicals. Mark et al.4 were unaware of the homolytic equilibrium 6 and therefore assumed that Φ(ONOO-)2-propanol Φ(ONOO-)no propanol represents the lower limit for Φ(1). They determined experimentally Φ(ONOO-)2-propanol ) 0.1 and Φ(ONOO-)no propanol ) 0.06 and calculated Φ(1) ) 0.09 using Φ(Fe2+) ) 1.25 for the ferrioxalate actinometer. Correction of the Φ(ONOO-) values by using the recently revised Φ(Fe2+) ) 1.4 at 254 nm21 yields 0.089 and 0.054, respectively. Hence, Φ(1) ) 0.089 - 0.054 ) 0.035 is in good agreement with the value reported in the present work. The buildup of ONOO- in alkaline solution containing 2-propanol deviates from linearity at relatively high dose as demonstrated in Figure 3, where the straight line corresponds to a constant Φ(2) ) 0.102. The deviation from linearity is significantly higher than that expected due to self-decomposition of ONOO- (kd ) 1.3 × 10-5 s-1) and its slow reaction with the produced acetone. It is attributed to the absorption of the 10600 J. AM. CHEM. SOC.
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(11)
Note that O2•- may also react with •NO2 to produce O2 and NO2- (reaction 7). From the material balance it follows that the total amount of •OH radicals must equal that of •NO2. In the presence of 2-propanol each •OH radical is converted into O2•-. Reaction 11 produces excess O2•- beyond the amount of •NO . The excess O •-, which is not removed by •NO , must 2 2 2 react with •NO to produce back the peroxynitrite since the competing O2•- dismutation reaction is orders of magnitude slower. The solid curve in Figure 3 represents the best fit calculated using Φ(2) ) 0.102, 253.7(NO3-) ) 4.25 M-1 cm-1, kd ) 1.3 × 10-5 s-1, and 253.7(ONOO-) ) 550 M-1 cm-1, where the latter value is in agreement with the literature one.25 Photolysis at 205-300 nm Using the Xenon Lamp. At 253.7 nm the π f π* and n f π* transitions overlap. Therefore, we extended our study to a wider range of excitation wavelengths to measure Φ(ONOO-)2-propanol at pH 13 and Φ(NO2-) at pH 4.2-4.5 in the presence of 10 mM formate. Photolysis of alkaline nitrate solutions with monochromatic light from the xenon lamp required longer exposure time compared to the low-pressure mercury lamp. Therefore, the calculation of Φ(2) should take into account the spontaneous decomposition of peroxynitrite according to eq 12. In this equation [ONOO-]t is the measured concentration at a given irradiation time, t, I is the absorbed dose rate in einstein L-1 s-1, and kd ) 1.3 × 10-5 s-1 is the apparent rate constant for the decomposition of peroxynitrite at pH 13.
Φ(2) ) ([ONOO-]t/I)(kd/(1 - e-kdt))
(12)
The dependency of Φ(1), Φ(2), and Φ(NO2-) on the excitation wavelength is summarized in Table 1. The yields of nitrite at 205 and 214 nm with and without interference filters were, within the accuracy of the measurements, the same indicating that the scattered light is coming from long wavelengths where both iodide-iodate and nitrate solutions are optically transparent. The dependency of Φ(1) and Φ(2) on wavelength is also illustrated in Figure 4. Madsen et al.6 reported that 48% ( 5% of the nitrate molecules excited at 200 nm produce the cis isomer of peroxynitrite, 8% ( 3% produce [NO + O2]-, and 44% decay to the ground state within 2 ps. [NO + O2]- denotes •NO + O2•- or NO- + O2, which probably recombine at longer time to form additional cis-peroxynitrite. If this is the case, the total yield of peroxynitrite should be Φ(2) ) 0.56 ( 0.08,6 which is considerably higher than the value Φ(2) ) 0.33 ( 0.03 presented in Figure 4. In addition, we observed the formation of •OH radicals with Φ(1) ) 0.13 ( 0.02 at near 200 nm, which is evident from the effect of 2-propanol on the measured peroxynitrite yield at pH 13. In view of these observations it is tempting to suggest that the absorption spectrum observed at (25) Logager, T.; Sehested, K. J. Phys. Chem. 1993, 97, 6664-6669. (26) Lo, W.-J.; Lee, Y.-P.; Tsai, J.-H. M.; Beckman, J. S. Chem. Phys. Lett. 1995, 242, 147-152.
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Table 1. Φ(1), Φ(2), and Φ(NO2-) at Various Wavelengths λ (nm)
Φ(NO2-)a
Φ(1)b
Φ(2)c
205 205d 210 214 214d 220 225 230 235 240 247 253.7e 260 270 300
0.207 ( 0.011 0.222 ( 0.002 0.198 ( 0.007 0.182 ( 0.005 0.175 ( 0.005 0.172 ( 0.008 0.152 ( 0.005 0.149 ( 0.004 0.122 ( 0.010 0.097 ( 0.002 0.084 ( 0.002 0.065 ( 0.002 0.047 ( 0.002 0.0197 ( 0.0008 0.0094 ( 0.0002
0.129 ( 0.055
0.278 ( 0.040
0.117 ( 0.020 0.10 ( 0.037
0.289 ( 0.013 0.294 ( 0.032
0.092 ( 0.025 0.082 ( 0.01 0.082 ( 0.022 0.069 ( 0.015 0.056 ( 0.012 0.048 ( 0.011 0.037 ( 0.004 0.024 ( 0.004 0.014 ( 0.002
0.284 ( 0.017 0.251 ( 0.005 0.239 ( 0.018 0.189 ( 0.005 0.147 ( 0.010 0.130 ( 0.009 0.102 ( 0.002 0.081 ( 0.002 0.0190 ( 0.0014
